1. Field of the Invention
The present invention relates to a linear actuator having a plurality of piston surfaces for providing a higher output force upon application of a pressurized fluid to a given diameter actuator. More particularly, the present invention relates to a pressurized-fluid actuator of compact size and that includes a movable cylinder having one or more axially spaced piston surfaces for applying an actuating force for movement of the cylinder in a retraction direction, and at least one additional piston surface for applying additional actuating force for moving the cylinder in an extension direction.
2. Description of the Related Art
Linear actuators incorporating pistons that move within cylinders upon application of a pressurized fluid are well known in the art and are used for many different purposes. Generally, the output force provided by such actuators can be increased either by increasing the pressure of the fluid supplied to operate the actuator, or by increasing the diameter of the piston to increase the surface area of the piston. However, some applications require the actuator to be contained within a very limited space (so that the diameter of the piston cannot be increased). In such applications, the pressure necessary to provide the required actuating force may exceed practical limits. Accordingly, an alternative design is needed that will provide the required actuating force in a limited space at a reasonable pressure.
A number of actuator constructions have been devised in an effort to respond to the shortcoming described above. Although the prior art discloses various devices for providing increased output force from a pressurized-fluid operated actuator, the devices typically either involve a complex mechanism or otherwise fail to reduce the size of the actuator sufficiently to enable its use in a confined space.
Briefly stated, in accordance with one aspect of the present invention an actuator is provided that includes a stationary cylinder of tubular form that defines an inner cylindrical surface. A movable cylinder is slidably carried within the stationary cylinder and has a rod affixed thereto, the rod extending from the movable cylinder in an axial direction relative to the stationary cylinder. The movable cylinder divides the stationary cylinder into an upper chamber and a lower chamber. The movable cylinder also includes an inner cylindrical space.
A fixed piston extends transversely across the inner cylindrical space of the movable cylinder, thereby dividing the inner cylindrical space into a first inner chamber and a second inner chamber. A first fluid conduit is in communication with the upper chamber of the stationary cylinder and with the first inner chamber of the movable cylinder. Supplying a pressurized fluid to the first fluid conduit thus initiates movement of the movable cylinder and rod in a forward direction relative to the stationary cylinder, thereby providing a rod extension stroke. A second fluid conduit is in fluid communication with the second inner chamber for moving the movable cylinder and rod in a reverse direction relative to the stationary cylinder when pressurized fluid is introduced, thereby providing a rod retraction stroke.
In accordance with another aspect of the present invention, the actuator includes a stationary cylinder containing a movable cylinder that is divided into multiple inner chambers by fixed (stationary) pistons. The inner chambers are in fluid communication with extension and retraction ports provided in the cylinder wall. Introduction of pressurized fluid into the retraction port causes the fluid pressure to act on xe2x80x9cnxe2x80x9d piston surface(s) to retract the movable cylinder and rod, while introduction of pressurized fluid into the extension port causes the fluid pressure to act on xe2x80x9cn+1xe2x80x9d axially-spaced piston surfaces to extend the movable cylinder and rod. Accordingly, the actuator provides an increased extension force without increasing the overall diameter of the actuator and without increasing the pressure of the fluid.